Conditioned well drilling fluid



PATENT OFFICE 7 2,271,695 CONDITIONED WELL anama FLUID Philip H. Jones,Bedondo Beach, Calif., or

to Union Oil Company of California, Los Angeles, Calif., a corporationof California No Drawing. Original application January 20,

' 1936, Serial No. 59,889.

Divided and this allplication January 14, 1938, Serial No. 185,008

6 Claims.

This invention relates to well drilling fluids, and particularly tofluids comprising solids in suspension in a liquid, for example, mudsordinarlly employed in connection with the drilling operations of oiland gas wells or otherborings through earth strata. This application isa division of my co-pending application Serial Number 59,889 forConditioned well drilling fluid, filed January 20, 1936. I

The objects of this invention are to provide a drilling fluid ofsufflcient weight'to insure proper control of the pressures of thepenetrated formation within the well, having formation sealingproperties which allow a minimum of loss of liquid to the penetratedformation, thin mud cake formation tendencies uponthe walls of thepenetrated formation, freedom from the tendency of gas-cutting and theattendant danger of loss ofcontrol of the. well, and having physical andchemical stability.

F This invention resides in a modified well drilling fluid comprising aheavy suspension of solids in a liquid to which has been added aformation penetration inhibitor orsealing agent. This invention alsoresides in a modified. well drilling fluid comprising a heavy suspensionof solids in a liquid to which has been added a formation drostaticheadof the mud fluid, it is desirable that this fluid should tics andweighting materials such as barytes.

hematite, and finely divided iron, maybe em-' ployed for such increasein density.

The existence of an excess of hydrostatic head of the drilling fluid inthe bore hole over that in the formation, however, results ordinarily in10 the penetration and loss to the formation of a quantity of the liquidportion of the drilling fluid and also results in the formation of acake of the solids on the formation wall from which the liquids havethus been removed by penetration or infiltration into the formation.Many This penetration of the liquid portion of the drilling fluid intothe exposed formation results in what has-commonly been known asswelling, J

caving, loss of circulation and damage to productive sands.

It has been discovered that certaih materials when added to the drillingfluid are effective in sealing and preventing or substantially inhibitvea maximum density I compatible with its other desirable characterisingthe penetration of the liquid from the ,{drilling fluid into the porousformations. Some of the most effective of these formation sealingsealing agent, and an anti-foaming agent. This invention morespecifically resides in a drilling fiuid comprising mud with admixtureof a small percentage of a formation sealing agent, an antifoamingagent, and a preservative.

In drilling wells for oil and gas by rotary tool methods it is commonpractice to circulate a drilling fluid known as the drilling mud downthe earthboring. "Ifhe circuiated drilling fluid serves to lubricate thedrill pipe, cool the bit, carry the cuttings out of'the, hole to thesurface,

and to seal and hold the penetrated formation 40 wall in place. It isalso an important function er the drilling mud to prevent'the escape ofgas and other high pressure fluids from the penetrated formations intothe bore hole. Sinceprevention of the entrance into the boreholes of thehigh pressure fluids is prevented bythe hyagents are, by way ofillustration, corn starch, wheat flour, quebracho andpsyllium seeds. Inpractice, it has been found necessary to add these substances to thedrilling mud in quantities 35 0.05 3.0 b w i ht the through the drillpipeand bit and return through rangmg mm m y e g mixed mud in order toreduce thepenetration of the formation by the drill mud liquid to asmall fraction of that resulting when untreated muds are employed in"drilling. The mud cake thickness formed on the formation wall is also atthe sametimegreatly reduced. 3

Table I indicates the efiectlveness of some of these materials inadmixture in small percentage with a typical drilling mud. in inhibitingflui penetration into drilled formations.

Table I watierlirriscedlfrom Th k Imam mu ug core 10 n m tat. es? t st;e he lb.l cu. it. seconds F. sg Tomlin llllriilagozr can?!" t 2hours 30min.

, Typical mud A j 73 1 32.2 200 2,000 29.8 18.5 0.21 Typical mud A+0.7%white flour. 71 8 27. 0 200 2, 000 15. 5 6. 1 Trace 'Iyp cal mudA+.,2.06% white flour-.. 2 30. 0 an 2, 000 14. 4 4. 8 Trace Typical mudA+2.D4% corn starch 69 6 30.0 200 1 2,000 ..ll. 5, 4. 2 Tracelypical mudA-H).25% (Qquebracho crystals.-- 74 2 33.0 200 2.D00 15.3 3.0 TracePercentages are by weight.

Corn starch was cooked in water atboiling temperature for 25 minutes.

a (a) zTan'bark extract.

( 008111188 mud.

A definition of Funnel Viscosity may be found in an A. P. 1. paper by H.N. Marsh and Harvey Lytel, October 1930. v

The white flour and corn starch may be prepared for use in thedrilling'fluid by first cooking in water at boiling temperatures forapproximately one half hour. may be added to the drilling mud eitherprior to or during circulation thereof to the drill hole byanyconvenient means. The flour or starch may be added in dry form directlyto the drilling mud,

.the drilling *mud asin the case of cooked" flour the formation. Whenthis over-balance of formation pressure obtains, the result is often ablow out in which the drilling fluid is ejected from the drill hole bythe gas pressure.

The paste thus formed" or starch. The psyllium seed flour may, however,

be added directly to the drilling mud in dry form in the mannerdescribed hereinbefore for flour and starch.

The quebracho crystals are soluble in the mud and may be added theretoin any convenient manner although it may be convenient to previthicknessof the formation could be recovered and accurately measured. The mudcake thick! nesses were determined by removing the test cores from thetesting apparatus and measuring themat the exposed edges. A morecomplete description of the above briefly described test method appearsin the American Petroleum Institute paper Evaluation of rotary drillingmuds by P. H. Jones and E. C. Babson.

When the drill penetrates deep strata con-- taining gas under highpressure gas tends to' enter the bore hole and dissolve in or mix withthe drilling fluid therein. As the fluid in its round of circulationmoves upward from the drill and the gas containing formation toward thesurface/the hydrostatic head of the fluid is progressively reduced, andthis results in a release and expansion of the included gas. Thisrelease and expansion of gas in turn results in the permeation of thedrilling fluid with gas bubbles which reduce its effective density andthis reduction of densityby gas permeation is known as gas cutting. Itis necessary, therefore, that the drilling fluid which is employed undersuch conditions be freed of gas at the, surface before it is againrecirculated to the gas containing formation where. additional gascutting results.

- Even though the amount of gas cutting of the drilling fluid is onlyslight at each cycle of cirreturnto the surface, for otherwise .it mayaccumulate to a degree where the gas cutting is suflicient to reduce theoverall density ,of the drilling fluid in the drill hole to such anextent that the hydrostatic-'headof the gas containing drilling-fluidmay be less than thatof the .eas in Ordinarily the gas is removedwithout special means by simply releasing the pressure on the mud at thesurface of the drill hole'and allowing the gas to extricate itself fromthe mud during a short period of relative quiescence or during the timeitis passing through the ditches: or sand separating apparatus. However,as the conditioned drilling fluids become more complex with resultingincrease of viscosity, immobility and thixotropic properties, it becomesmore difficult to effect a satisfactory separation of the gas. This isparticularly true in the present case where formation penetrationinhibiting agents are utilized in admixture with the drilling fluid.

-When the hereinbefore enumerated formation penetration inhibitingagents were utilized in admixture with drilling muds comprising solidsin suspension in water and when they were exposed to conditions tendingto cause gas cutting, a marked tendency to form stable gas-cut mud andfoam was observed.

When stable gas-cut mud and foam is formed as a result of the presencein the drilling fluid under gas-cutting conditions of the hereinabovedescribed formation penetration inhibitors, no practical amount ofquiescence, agitation or circulation thereof in the ditches at thesurface as heretofore commonly employed for the separation of gas, willeffect. satisfactory separation of the gas and reduction of the foam.,The employment of formation penetration inhibitors alone undergas-cutting conditions and other conditions conducive to gas-cutting andfoaming in the drilling fluid is therefore impractical.

It is necessary, therefore, in order to make practical use of theconditioned mud having desirably low formationpenetratingcharacteristics' and containing formation penetrationinhibitors,. 'to combine therewith anti-gas-cutting agents,

which are effective in counteracting the increased gas-cutting andstable foam-forming tendencies imparted to the drilling fluid by thepre's'ericeof such formation penetration inhibitors.

Anti-gas-cutting agents which may be added in small quantities varyingfrom 0.03% to 1.00% by weight; of the drilling fluid and which have beenfound to be effective particularly in combination with chilling fluidscontaining formation penetrating inhibitors, or formation sealingagentsare-high boiling point alcohols, for example, thealiphaticalcohols, such as octyl alcohol and the alcohol of the terpene seriessuch as fenchyl alcohol; glycerin and other polyhydric alcohols; thefatty-acids, coconut oil fatty acid, capryllic acid and the hydroxy andunsaturated derivatives of fatty acids such as castor oil acids; theesters, glycokoleate, butyl stearate and glycer'ol monoricinoleate; thealcohols of the ter- 4 penes; .terpineol and pine oil and fenchylalcohol,

culation, it isimportant that it be freed at each and' waxes such asmontan wax in mineral seal oil. Octyl alcohol and other alcohols of theallphatic series having low solubilities in water and marked andfavorable surface tension modifying effects are particularly effectivein this respect.- The anti-gas-cutting agents can be broadly classifiedas anti-foaming agents with the above subclassifications.

Table II indicates the beneficial effect of oertainpf the most effectiveones of the hereinbefore enumerated anti-gas-cutting agents uporf mudswhich'have been gas-cut and subsequently uniformly treated by agitation.and settling to remove the included gas.

drilling fluid, colloidal or non-colloidal in type,

Table II Results of tests on gascut mnd Initigl 1st period of 2nd periodof y Boiling point of Gascut conditioned mud containing lb./cu. ft a aformation penetration inhibitor Bgmtmn at 80 F. gas 3 i before gasagent,

Gravity, Temp., Gravity,- Temp., cumng lb./cu. it. F. lb./cu. it. F.

l Mud B l-1.0% flour 40. 145 40. 0 125 70.0 2 Same as girl-0.2% castoroil fatty acid. 65. 145 67. 0 128 70. 0 482 mm Hg 3 Same as l)+0.1%glycol oleate 61. 0 148 63.0 123 70. 0 Above 400 '4 Same as (l)+0.l%butyl stearate 64. 5 142 68. 5 118 70.0 428 mm Hg 5 Saline ale (1) +O.l%glycerol mono- 62. 0 140 65. 0 120 70. 0- Above 400.

r cino eate. A 6 Same as (i)+0.2% coconut fatty acid. 63.0 140 65.0 12070.0 356 16 mm. Hg. 7 Mud D+2.0% cooked Starch.. l 7 m0 130 40. 0 78 75.0 8 Same as (7)+0.0,3% octyl alcohol. 61. 5 118 64.0 110 75.0 384.

(B) Coalinga red mud+2% aqua gel+.l% cresylic acid.

(D) Typical mud, origin unknown.

It is important that the anti-gas-cutting agents to be added incombination with the formation penetration inhibitors to the mud, haveboiling ing fluids where temperatures are on the. average favorable forbiochemical changes it has been necessary to alsoremploy in admixturetherewith suitable germicldes or preservatives. Such preservatives whichhave been efiective in preserving the desirable characteristics of theconditioned mud are phenol, cresol, ci'esylic acid, benzoate of soda andzinc chloride inquantities approximating 0.1% by weight of the drillingfluid.

Other formation sealing agentswhich are effective in admixture with themud or drilling fluid und r certain conditions are listed together withthe store-mentioned preferred'formation sealing agents under theirvarious physical and chemical classifications as follows: the proteincolloids, glue, casein, milk powder, blood albumin and gelatin; thecarbohydrate colloids, gum arable and gum copal; the gelatinousvegetable pastes or slimes, seaweed (algenic acid); agar 'agar,cottonseed meal, linseed cakes, wheat flour. corn starch, quebracho andpsyllium seeds; the sugars, dextrose, molasses and corn syrup-y. the

waxes, montan wax and the soaps such as saponii fied montan wax. h

All of these. formation sealing agents can be broadly classified asorganic colloids with .the'

hereinbefore enumerated subclassiflcations.

. The mechanism responsible for the successful performance of theformation sealing agents such as the starchyand pasty materials andorganic colloids in general may probably be dueto the effects associatedwith the combination of hydrophilic colloids such as these with the hy-'vdrophilic type of-colloids usually present in drilling muds.

These formation penetration inhibitors and anti-gas cutti ng agents.have been effectivewith various drilling fluids having differentcompositions, but thesedrilling fluids generally-comprise aqueoussuspensions of solid matter such as clay, bentonite, etc.

' formation penetration and low gascutting tenddrilling operations.

is efiective in preventing the penetration of the drilled formationswith the liquid portion of the drilling fluid, and the attendantweakening and frequent caving of the. drill hole walls upon such ingfluid of proper formation sealing properties while at the same timeinsuring suflicient freedom from gas-cutting and the maintenance ofsufficient density and stability. This invention also reduces to aminimum the detrimental effect of drillingiluids upon producing horizonsduring I not to be limiting but-may include all processes, drillingfluids and materials within the scope of the claims.

I claim:

1. An improved well drilling fluid'having low gas-cutting tendenciescomprising an aqueous suspension of heavy solids to which has been addeda modicum of a'fatty acid of the class consisting of coconut oil fattyacid, cap'ryllic acid and-caster oil acid. v 2. An improved welldrilling fluid having low gas-cutting tendencies comprising an aqueoussuspension of heavy solids to which has been added a'modicum of coconutoil fatty acid.

3. An improved well 'drilliiig fluid having low gascutting tendenciescomprising an aqueous suspension of heavy solidsyto which has been addeda. modicum of caster oil'fatty acids.

4r An improved well drilling fluid having low gas-cutting; tendenciescomprising an aqueous suspension of heavy solids to which has been addeda modicum of capryllicacid: I

5, An improved ,well drilling fluid having 10 The foregoing is enciescomprising an aqueous suspension of heavy solids, an added gelatinousorganic formation penetration inhibitor in suflicieiit quantityto impartformation sealing properties to th mixf ture and a modicum of afatty.acid'of the class consisting of coconut oilfatty acid, capryllie acidand caster oilsacid;

' tion penetration inhibitor 1 contains. istarch.

" mm H; JouEs.

This invention, however, whenapplied to any

